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Buckling tests of cylindrical composite shells in multiaxial loading
No full textThin-walled cylindrical composite shells are prone to buckling failure in a variety of load cases. The number of influencing factors and comparably small amount of test data on combined load cases, which regularly occur in application, pose a major design challenge. Two experimental campaigns on the buckling of thin-walled cylindrical composite shells in multiaxial loading are carried out with two nominally identical specimens with a radius-to-thickness ratio of 375. The results of buckling tests with combined axial compression and torsion, compression and bending, as well as all three buckling critical load types are presented. The influence of the loading direction of bending and torsion is shown, and the effects of repeated mounting of the specimens in the test rig as well as the scatter of buckling loads are discussed. Comparison of test results with the established NASA SP-8007 guideline and perfect buckling loads shows major qualitative and quantitative differences in the load interaction curves
Resource-efficient use of single-use surgical textiles
No full textOperationssäle gehören zu den ressourcenintensivsten Bereichen des Krankenhauses und verursachen erhebliche Mengen an Abfall und CO2-Emissionen. Einweg-OP-Textilien tragen hierbei wesentlich zum ökologischen Fußabdruck chirurgischer Eingriffe bei. Die Urologie leistet als operativ geprägte Disziplin einen bedeutenden Beitrag zum OP-Aufkommen. Ziel dieser Studie war es, den Beitrag von OP-Textilien zum Ressourcenverbrauch zu quantifizieren und zu analysieren, in welchem Umfang durch eine standardisierte Nutzung ökologische und ökonomische Einsparpotenziale realisiert werden können. Grundlage bildeten Verbrauchs- und Leistungsdaten (OPS-Ziffern, Operationen- und Prozedurenschlüssel) von 25 Krankenhäusern (in 4 Versorgungsstufen) einer deutschlandweit tätigen Klinikkette in privater Trägerschaft. Der tatsächliche Verbrauch aus dem Jahr 2022 wurde einem Soll-Szenario mit vordefinierten OP-Standards gegenübergestellt. Für jeden Standard wurden CO2-Emissionen mittels „life cycle assessment“ berechnet und den jeweiligen Operationen zugeordnet. Im Jahr 2022 wurden in den 25 untersuchten Kliniken 213.048 Operationen durchgeführt. Dabei wurden insgesamt 352,7 t Einweg-OP-Textilien verbraucht, was 1997 t CO2-Äquivalenten entspricht. Rohmaterialien verursachten dabei den größten Anteil der Emissionen, während Transporte nur einen geringen Beitrag leisteten. Durch die konsequente Standardisierung könnte der CO2-Ausstoß um bis zu 8 % reduziert werden. Besonders hohe Einsparpotenziale wurden in orthopädischen (bis zu 23,4 %) und kardiologischen Kliniken (bis zu 20,6 %) identifiziert. Die Ergebnisse zeigen, dass ein Teil des Ressourcenverbrauchs im OP vermeidbar ist. Standardisierte Nutzung von Einweg-OP-Textilien bietet sowohl ökologische als auch ökonomische Vorteile
Robust tracking with particle filtering for fluorescent cardiac imaging
No full textIntraoperative fluorescent cardiac imaging enables quality control following coronary bypass grafting surgery. We can estimate local quantitative indicators, such as cardiac perfusion, by tracking local feature points. However, heart motion and significant fluctuations in image characteristics caused by vessel structural enrichment limit traditional tracking methods. We propose a particle filtering tracker based on cyclicconsistency checks to robustly track particles sampled to follow target landmarks. Our method tracks 117 targets simultaneously at 25.4 fps, allowing real-time estimates during interventions. It achieves a tracking error of (5.00 +/- 0.22 px) and outperforms other deep learning trackers (22.3 +/- 1.1 px) and conventional trackers (58.1 +/- 27.1 px)
Hidden regularity in singular optimal control of port-Hamiltonian systems
No full textWe study the problem of state transition on a finite time interval with minimal energy supply for linear port-Hamiltonian systems. While the cost functional of minimal energy supply is intrinsic to the port-Hamiltonian structure, the necessary conditions of optimality resulting from Pontryagin's maximum principle may yield singular arcs. The underlying reason is the linear dependence on the control, which makes the problem of determining the optimal control as a function of the state and the adjoint more complicated or even impossible. To resolve this issue, we fully characterize regularity of the (differential-algebraic) optimality system by using the interplay of the cost functional and the dynamics. In case of the optimality DAE being characterized by a regular matrix pencil, we fully determine the control on the singular arc. In case of singular matrix pencils of the optimality system, we propose an approach to compute rank-minimal quadratic perturbations of the objective such that the optimal control problem becomes regular. We illustrate the applicability of our results by a general second-order mechanical system and a discretized boundary-controlled heat equation
Design of a high-performance tensor–matrix multiplication with BLAS
No full textThe tensor–matrix multiplication (TTM) is a basic tensor operation required by various tensor methods such as the HOSVD. This paper presents flexible high-performance algorithms that compute the tensor–matrix product according to the Loops-over-GEMM (LOG) approach. The proposed algorithms can process dense tensors with any linear tensor layout, arbitrary tensor order and dimensions all of which can be runtime variable. The paper discusses two slicing methods with orthogonal parallelization strategies and propose four algorithms that call BLAS with subtensors or tensor slices. It also provides a simple heuristic which selects one of the four proposed algorithms at runtime. All algorithms have been evaluated on a large set of tensors with various tensor shapes and linear tensor layouts. In case of large tensor slices, our best-performing algorithm achieves a median performance of 2.47 TFLOPS on an Intel Xeon Gold 5318Y and 2.93 TFLOPS an AMD EPYC 9354. Furthermore, it outperforms batched GEMM implementation of Intel MKL by a factor of 2.57 with large tensor slices. Our runtime tests show that our best-performing algorithm is, on average, at least 6.21% and up to 334.31% faster than frameworks implementing state-of-the-art approaches, including actively developed libraries such as Libtorch and Eigen. For the majority of tensor shapes, it is on par with TBLIS which uses optimized kernels for the TTM computation. Our algorithm performs better than all other competing implementations for the majority of real world tensors from the SDRBench, reaching a speedup of 2x or more for some tensor instances. This work is an extended version of ”Fast and Layout-Oblivious Tensor–Matrix Multiplication with BLAS” (Başsoy 2024)
A global analysis of the influence of shallow and deep groundwater tables on relationships between environmental parameters and heatwaves
No full textHeatwaves increasingly impact ecosystems, human health, and economic activities worldwide. As their frequency and intensity rise, understanding the mechanisms driving heatwave dynamics and interactions with land surface processes becomes crucial. While numerous studies have examined atmospheric and land surface variables, the role of groundwater, through its effects on soil moisture and surface evaporative fluxes, remains less understood. Although modeling approaches at various scales have enhanced our understanding of groundwater-atmosphere coupling, machine learning (ML) enables capturing complex, nonlinear interactions and evaluating the relative importance of key drivers globally. We developed pixel-based ML models to estimate global summer heatwave frequency over the past 21 years. For each pixel, we considered data within a 1.5° radius (149 neighboring pixels), identified as the optimal scale through a saturation radius analysis. We used feature importance metrics to identify the dominant drivers among surface fluxes, land characteristics, atmospheric and hydrological variables, and interpreted these results in relation to contrasting groundwater depths (100 m). We ensured robustness using 10-fold cross-validation and confirmed that results were not driven by randomness with two additional validation runs on a subset of the data, with shuffled targets and randomized covariates. Our findings suggest that geopotential height showed the highest relative importance among predictors in regions with deep groundwater tables, while in areas with shallow groundwater, surface fluxes emerge as the key contributor. Incorporating groundwater-related processes may therefore improve understanding of land-atmosphere interactions and support more robust assessments of future heatwave risks
Conceptual design and energy management analysis of turbofan-based hybrid-electric propulsion
No full textHybrid-electric propulsion systems offer the potential to make aircraft more efficient by using electric energy to cover a share of the total energy demand. However, resolving questions related to aircraft hybridization, namely the potential fuel consumption benefits and the energy management throughout the mission, is vital. This highlights the importance of holistic evaluation methods. Hence, this paper introduces a method for the design and evaluation of hybrid-electric propulsion systems. The method enhances current sizing methods by modeling a hybrid-electric turbofan and estimating electrical losses for the electric power train to explore hybrid energy management strategies. The method is demonstrated using the short–medium-range concept aircraft D239. Initial simulations indicate a total increase in the block fuel mass of approximately 2.7% with constant hybridization throughout the 800 n mile reference mission. However, optimizing the energy management strategy reveals an improved result of a 1.6% increase in mission block fuel. Key factors contributing to this improvement include using hybrid-electric power exclusively during the climb phase, shorter mission ranges, and omitting battery charging during flight. However, an overall increase in the block fuel mass persists under realistic assumptions. This highlights the need for further exploration of hybrid-electric concepts and methodical refinement
Algebraic and algorithmic synergies between promise and infinite-domain CSPs
No full textWe establish a framework that allows us to transfer results between some constraint satisfaction problems with infinite templates and promise constraint satisfaction problems. On the one hand, we obtain new algebraic results for infinite-domain CSPs giving new criteria for NP-hardness. On the other hand, we show the existence of promise CSPs with finite templates that reduce naturally to tractable infinite-domain CSPs in the scope of the Bodirsky-Pinsker conjecture, but that are not finitely tractable, thereby showing a non-trivial connection between those two fields of research. In an important part of our proof, we also obtain uniform polynomial-time algorithms solving temporal constraint satisfaction problems
Wärmebereitstellung aus erneuerbaren Energien
No full textIm folgenden Kapitel wird ein Überblick über die wichtigsten Optionen zur Bereitstellung von Wärme aus erneuerbaren Energien gegeben. Die dominierende Technologie ist dabei die Biomassenutzung – und hier insbesondere die Nutzung von biogenen Festbrennstoffen. In den vergangenen Jahren stieg zudem der Anteil der Umweltwärmenutzung (d. h. Wärmepumpenapplikation) deutlich an – und das mit einem anhaltendem Trend
Modellierung realitätsnaher Greifkraftverläufe aus Bohrhammeranwendungen zur Bestimmung der mechanischen Impedanz mit einem translatorischen Shaker-System
No full textAs part of this work, a study was conducted in which the statistical deviation of the grip force applied by the test subject was measured in comparison to the specified, time-varying grip force on an ISO standard grip. For example, these measurements were also taken under a multi-sine deflection of the ISO standard grip in the translational direction in order to initiate vibrations on the hand-arm system of the test subjects. The vibration behavior of the human hand-arm system (HAS) in response to external vibrations and grip forces can be described in the frequency range by the mechanical impedance (MI). The measured mechanical impedance then serves as a requirement parameter for the development of physical-dynamic hand-arm models (HAM). These hand-arm models can be used in product development to simulate human behavior and investigate correlations between technical products and human behavior without having to take real humans and their disturbance variables into account.
The central challenge is that many variables have an influence on the mechanical impedance of the HAS. In addition to interaction forces such as grip and push forces, their dynamic progression during a use case also has an influence. The app interface developed in this research project and its verification should make it possible to map this influence in both physical and virtual HAMs.
The results of the work show that the modeling and graphical representation of dynamic grip forces and their measurement work in a statistically significant way. The 13 test subjects were able to follow the complex, changing grip force curves with a maximum error of 16.16 N. It was demonstrated by way of example that the grip force curves can also be followed under translational excitation. This enables the measurement and recording of the passive behavior of test subjects with grip forces that change over time. The changing grip force curves can be measured in real-world applications. The resulting requirements, in turn, serve to develop dynamically adaptive hand-arm models.Deutsche Forschungsgemeinschaft (DFG